UV unwrap not working?
I wasn't aware of this behavior myself so far to be honest, but I was able to replicate what you described on a simple cylinder with a few loop cuts on the side. The first face ring would unwrap no problem, but all the others would fail. At least the command seems to do nothing.

Here's a small video demonstrating the behavior:



In fact, it does perform an unwrap, but it is scaling all resulting UVs to zero.

To fix it, perform any other unwrap on the whole mesh before you start the Follow Active Quads method. For example, use Smart UV project. Afterwards, you can unwrap ring by ring.



Of course, it is also possible to unwrap more than one ring at once: